Human operators often operate heavy machines. To safely operate these machines, human operators need to be mentally alert and focused. However, many factors may cause the machine operators to lose their mental alertness and focus while operating the heavy machines, thereby creating hazard or even deadly situations. For example, operators of transportation vehicles such as automobiles, trucks, trains, airplanes, and ships may doze off due to fatigue or sleep deprivation, thereby creating dangerous situations to the surroundings. In fact, many major accidents occur because operators of transportation vehicles fell asleep during work. Further, operators of transportation vehicles sometimes may also operate under chemical influences. For example, a driver of a vehicle may drive under the influence of alcohol or drugs. In these situations, the operators may also lose his or her mental sharpness and focus, thereby creating dangerous situations.